Flexible, reinforced piping, particularly that used to convey petroleum effluents, conventionally has sealing sheaths made from thermoplastic materials, which offer the specific advantages of providing a high degree of mechanical deformation and being easy to use with extrusion processes.
However, they do have significant limitations, the main ones being:
limitations in terms of characteristics, depending on the temperature;
they are not fully impermeable to gas (due to diffusion over time), particularly in respect of H2S, which gives rise to a serious problem since it can lead to corrosion of the metal materials placed on the exterior of these sheaths. These materials, used to make the reinforcement designed to withstand pressure and traction, must by definition retain their original characteristics over time.
Metal materials are known to be impermeable to gas and are able to withstand the maximum temperature which a petroleum effluent might reach without any major problem. However, they are not flexible or are only slightly flexible as compared with polymer plastics materials. However, there are numerous applications (coiled tubing for drilling, rigid piping which is unwound at sea for transporting petroleum effluents) where steel tubes can be bent across small radii of curvature, chiefly by deformation in the plastic domain of the material.
Attempts have been made in the past to use continuous corrugated tubing as a means of making the piping more flexible but in this case, the need to be able to withstand resistance to internal pressure means that for these applications, it is necessary to strengthen the hollows of the corrugations, using a composite fibre material impregnated with thermo-setting resin as a reinforcement.
The objective of the present invention is to provide a reinforced flexible pipe. The piping consists of a combination, from the axis of the pipe out towards the exterior, of a cylindrical metal, inner tube which provides a seal against the effluents conveyed by the pipe, a layer which is resistant to internal pressure and external pressure consisting of reinforcements wound in a small pitch spiral around said inner tube and a sealing sheath made from an extruded plastics material.
In one embodiment, the structure of the pipe may include an intermediate layer made from plastic and inserted between the inner tube and the pressure-resistant layer.
The intermediate layer may be extruded on said continuous tube.
The intermediate layer may consist of a strip wound around the continuous-tube.
The pipe may have at least one layer of reinforcement which is resistant to traction, disposed on the outside of the pressure-resistant layer. The sealing sheath may be disposed between the pressure-resistant reinforcing layer and the traction-resistant reinforcing layer.
The sealing sheath may be arranged on the exterior of the traction-resistant reinforcing layer.
The sealing sheath may be externally protected by a flexible metal layer, for example clamped strapping. The pipe may have two sealing sheaths, one directly on top of the pressure-resistant layer and the other above the layer of traction-resistant reinforcement.
The profile of the pressure-resistant strengthening may be T-shaped.
The structure of the flexible piping of the invention described below allows a thin cylindrical tube of a metal material, selected so as to be resistant to corrosion (for example stainless steel or titanium), to be inserted in a flexible assembly consisting of reinforcement resistant to pressure, both internal and external, reinforcement resistant to longitudinal forces and plastic sheaths, either external or inserted in the middle. Said flexible structure is of a size such that it will comply with specifications corresponding to the requirements for pipe-laying and servicing on the sea bed, this piping being substantially horizontal and used to convey corrosive effluents. In most cases, said flexible tubing is laid in a trench (known as a xe2x80x9cbedxe2x80x9d) and then covered with materials designed to prevent, the flex-pipe from buckling, i.e. from extending and creating vertical loops under the force of the internal pressure whilst the two ends remain blocked.